The invention relates to a semiconductor structure, particularly for use in a semiconductor detector according to the invention.
The use of so-called drift detectors for radiation detection is known which detectors are described, for example, in L. STRÜDER: “Nuclear Instruments and Methods in Physics Research A”, Vol. 454, 2000, DE 34 27 476 A1 as well as in DE 102 13 812 A1. In this case, the radiation to be detected produces signal electrons in a weakly doped and depleted semiconductor substrate, several ring-shaped and concentrically arranged electrodes being located at one surface of the semiconductor substrate, which electrodes produce in a semiconductor substrate a drift field, through which the signal electrons produced by the radiation drift to a centrally arranged read-out element that detects the signal electrons and, subsequently, the taken-up radiation.
The read-out element can consist here of a DEPFET transistor (DEPFET—Depleted Field Effect Transistor) which was invented in 1984 by J. Kemmer and G. Lutz. Such a DEPFET transistor can have a weakly n-doped, depleted semiconductor substrate, a highly p-doped rear electrode being arranged on one surface of the semiconductor substrate, which rear electrode forms a diode poled in the blockage direction with the weakly n-doped semiconductor substrate and serves the purpose of depletion of the semiconductor substrate, wherein holes originating in the semiconductor substrate as a result of radiation effect are suctioned off by way of the rear electrode from the semiconductor substrate.
On the opposing surface of the semiconductor substrate where a DEPFET transistor is concerned, there is a highly p-doped source region and also a highly p-doped drain region, a channel being located between the source region and the drain region, and the conductivity of this channel can be set by a gate electrode that can be externally activated.
In the semiconductor substrate a weakly n-doped inner gate region is located below the channel, in which there is a gathering of signal electrons originating in the semiconductor substrate as a result of the radiation effect. The electric charge accumulated in the inner gate region controls the conductivity of the channel between the source region and the drain region in a similar manner to that of the external gate electrode, so that the drain-source-current is a measure for the detected radiation.
However, the signal electrons gathered in the inner gate region must be removed occasionally from the inner gate region in order to maintain the sensitivity of the drift detector. For this purpose, a separate clear contact is envisaged with the known DEPFET transistors that is located on the source side next to the DEPFET transistor itself and which suctions off the signal electrons gathered in the inner gate region with the application of a positive electric voltage.
A disadvantage with this known structural configuration of a DEPFET transistor is the fact that high electric voltages are required for clearing, whereby a complete removal of the signal electrons gathered in the inner gate region is often not even possible at all.
The invention is therefore based on the task of creating a semiconductor structure according to a DEPFET transistor where a complete and thorough clearing to the greatest possible extent is enabled with lesser levels of electric voltages.